A small plane went down in the Gulf of Mexico on Thursday about three hours after two F-15 fighter jets tried to make contact with the unresponsive pilot, authorities said.

Two jets caught up with the Cessna 421C at 8:45 ET and were flying with it and monitoring it but hadn't been able to hail the pilot, said North American aerospace defense command spokesman John Cornelio.

The two F-15s from the New Orleans national guard were already on a mission over the gulf, coast guard chief John Edwards said in a news release. The Jacksonville air traffic control center asked the military if jets could check on the plane that was orbiting near one of Eglin air force base's warning areas over the gulf, Edwards said. Eglin is located on Florida's panhandle.

The jets' pilots reported that the Cessna's windshield was iced over and that the plane was fluctuating between 25,000 and 35,000 feet.

The Cessna went down at about 12:10pm, some 120 miles west of Tampa, Florida, said petty officer Elizabeth Boderland with the coast guard in New Orleans.

The plane landed softly in the water and was intact, floating right side up, Boderland said. A coast guard helicopter was responding, and a patrol boat was about 90 miles away. Boderland did not know the condition of the pilot.

"The situation is pretty dynamic right now," Boderland said.

Federal aviation administration (FAA) spokeswoman Kathleen Bergen said the plane was flying from Slidell, Louisiana, to Sarasota, Florida. She says one person was on board and that the FAA had been tracking the plane since it lost contact with the pilot at 9am.

Federal aviation administration records show that the Cessna was registered to Lee H Aviation in Wilmington, Delaware. The address listed on the FAA registry corresponds with that of Delaware Registry Ltd, a company that provides corporate services and registers both airplanes and yachts. A woman who answered the phone at Delaware Registry said the company does not give out information about its clients.